(a) Field of the Invention
The present invention relates to an overcurrent protection structure and a method and an apparatus for making the same, and more particularly to an overcurrent protection structure, which can ensure that the overcurrent protection structure would blow at high temperature when reaching a specific current or a specific temperature and the protection effect against excess current, and a method and an apparatus for making the same.
(b) Description of the Prior Art
A fuse is designed to protect electric circuits or electrical equipments in an electric circuit from the damage on sophisticated electronic instruments caused by an instantaneous excess current or an excess voltage. Therefore, the fuse is a necessary electronic component. A conventional fuse unit has a coil or a fuse material, and the fuse material is sealed in a tube made of hard glass, ceramic or other insulating materials. The insulating tube is filled therein with an inert gas or an arc resistant packing material. The both ends of the tube are electric conductors respectively, and the current can flow through the fuse by the connection of the electric conductors to the soldering joints on a circuit board. When an instantaneous current exceeds the predetermined current rating, the fuse material will blow at high temperature due to the heat induced by the instantaneous excess current so as to break the circuit. Thus, the excess current would stop flowing into the circuit to protect the electric circuits and electrical equipments from damage. When a fuse unit of such structures is used at a larger current (240 A) or at a high voltage (2250 V), the instantaneously generated energy would result in the high heat of the fuse blowout such that the surrounding media will expand rapidly and burst the tube. In the meantime, the arcs will occur so that it is easy to burn out the peripheral electronic components and damage expensive system equipments.
Therefore, the conventional structures of fuse unit and their manufacturing method mostly emphasize the suppression of arcs, such as U.S. Pat. No. 6,507,264, U.S. Pat. No. 5,572,181, U.S. Pat. No. 5,923,239, U.S. Pat. No. 6,507,265, U.S. Pat. No. 5,812,046, U.S. Pat. No. 5,596,306, and the like but their processes are relatively complicated. Accordingly, TW Patent 200727319 proposed an overcurrent protection element, as illustrated in FIG. 1. The overcurrent protection element 1 comprises a fuse body 11 and a fuse coating 12, wherein the both ends of the fuse body 11 respectively extend outwardly beyond the fuse coating 12 and form a first electrode 13 and a second electrode 14, and the fuse coating 12 is composed of a polymeric material. When the overcurrent protection element is in a condition of excess current, the fuse coating 12 can absorb the heat generated by the blowout of the fuse body 11 and suppress the occurrence of arcs.
However, in reality, when the fuse body 11 is electrically energized and generates heat, a part of the heat will dissipate through the heat conduction of the fuse coating 12 due to the contact of the fuse body 11 with the fuse coating 12 so that when a set excess current flows through the fuse body 11, the fuse body 11 cannot reach a specific current or a specific temperature and blow at high temperature. As a result, it is unable to achieve the circuit protection effect against excess current such that the electronic circuits of electrical devices would be damaged or burned out.